The invention relates to a microwave oscillator, which can be tuned by varying a magnetic field, using magnetostatic waves which can be transmitted in a thin layer of magnetic material.
In optics and acoustics, it is known to reflect a wave guided in a layer of an appropriate material by a grating formed in said layer. The transmission velocities of light waves and also sound waves are linked with the characteristics of the material constituting the layer and with the physical phenomenon in question. The pitch of the periodic structure defines the wavelength of the waves likely to be reflected. A resonator is formed by producing two systems between which the waves can be under standing wave conditions.
In order to obtain wave frequencies in the microwave range (typically 1-10 GHz), it is possible to use the transmission of so-called magnetostatic waves in a magnetic material. These waves, which are purely of the magnetic type, are due to the movement of the magnetization in the material. They are recited by means of a tranducer in which a microwave current circulates. The resonant frequency which can be obtained in a cavity between two systems is of the order of 1 GHz. This frequency can be made variable by modulating an external magnetic field. In general, such a resonator permits several oscillation modes in its pass band, the frequency spacing of these modes being inversely proportional to what is called the equivalent length of the cavity. For a given length, the number of modes is determined by the reflection pass band of the systems. To obtain a monomode oscillator from such a resonator, it would theoretically be possible to reduce the value of the equivalent length in order for there to be only a single mode in said pass band. However, the reduction in this value leads to a reduction in the quality of the resonator, which is incompatible with acceptable performances.